This invention is directed to a method for carrying out environmentally safe well work-over operations on a multi-well offshore platform to prevent pollution of a body of water with hydrocarbons, wherein the platform is equipped with an oil-and-water treating system of normal capacity for treating all of the hydrocarbon-bearing production well fluid flowing from all of the wells.
It is conventional in oil and/or gas drilling and production operations to collect rainwater, deck-flushing water and miscellaneous fluids such as engine oil and greases from the decks of an offshore platform. Typically, a plurality of drains are arranged throughout one or more decks of the offshore platform, especially on portions of the decks which are open and therefore exposed to the weather. Since the rainwater washes any spilled oil or grease off of the deck and into the drains, the rainwater cannot be passed directly into the ocean beneath the platform (see for example OCS order No. 7 published in the Federal Register on May 18, 1979). Instead, the collected rainwater must be treated so as to separate the oil from the water until the percentage of oil in the water reaches an acceptable level. Typically, (as the governing country's ordinances permit) as little as 48 to 72 ppm of oil is permitted in the water to be returned to the ocean beneath the platform.
During operation of the oil and/or gas processing facility, it is conventional to pass the produced fluid through a three-phase separator to divide the fluid into gas, oil and produced water and solid particles (sand) components. The produced water, however, contains enough oil, oily sand and other contaminants sometimes to require further treatment of the produced water before being returned to the surrounding ocean. As with the collected rainwater, typically, as little as 48 to 72 ppm of oil is permitted in the water and solid particles (such as sand) to be returned to the ocean beneath the platform.
Sometimes, the recovery of the oil present in the collected water from the drains and the produced water from the three-phase separator is economically worthwhile because of the value of the recovered oil. Both for pollution prevention and for economical reasons, it has been conventional to supply collected rainwater and oils from the decks of an offshore platform and the produced water from a three-phase separator to a "Skim Pile" (hereinafter skim pile) or elongate separator conduit of Engineering Specialities, Inc., Covington, La., such as is described in U.S. Pat. No. 3,893,918. A complete oil-and-water separator system as normally used on offshore platforms is described in detail in U.S. Pat. No. 4,428,841, issued to Uncas B. Favret, Jr.
Such oil-and-water separator systems are engineered, sized, designed and tuned to handle the anticipated flows of oil, gas and water from one or more wells in a manner such that any oil in the water being discharged to the ocean will be within the limits required in the environmental regulations set by the federal, state or local authorities. Any time a new well is put on production and its flow sent to the normal oil-and-gas separator, the resultant changes in the volumes of oil and water handled by the separator system may require adjustment of the separator system controls to fine-tune the separator system.
Problems arise from time to time with a platform's separator system when it is necessary to work over one or more of the wells on the offshore platform. Work-over operations may include shutting in a well, pulling the production pipe string from a well, acidizing a well, or killing a well by pumping into it water, sea water, drilling mud, completion fluid, or solutions of sodium chloride, calcium chloride, calcium bromide or zinc bromide. Large volumes of fluids which may not be compatible with those handled by the platform's oil-and-water separator system may also be generated during recompleting a new zone in a well, by producing work-over fluids when a well is first put on production, when squeezing cement during abandonment of a well, when replacing downhole equipment such as gas lift valves, or when hosing down equipment as it is withdrawn from a well.